Golf clubs undergo many stresses when they strike a golf ball. The face undergoes compressive impact forces as it strikes the ball, the sole undergoes compressive and lateral impact forces as it strikes the ground during the downstroke, and the hosel undergoes twisting and torsional forces as the shaft brings the club head through the stroke. The transitional portions of the club head, e.g., the face/crown interface, also experience tremendous stress because of the convergence of different types of force from multiple directions. Furthermore, after the initial impact, a good deal of energy from the impact is dissipated as vibration through the club head.
To survive repeated striking, a golf club head must be strong and have good energy-damping properties. However, a golf club head must also be lightweight, allowing a golfer to achieve head speeds of 100 miles per hour, or greater. In view of these needs, golf club manufacturers typically use materials such as aluminum alloys, steels, and titanium alloys, which provide a desirous balance of weight and strength. Nonetheless, there is no perfect material from which to make the entire club head—each material has unique properties, such as weight, tensile and compressive strength, and flexibility. Clubs made from a single material will excel in some areas (e.g., face hardness), while faring poorly in others (e.g., flexibility). For example, it is beneficial to use hardened steel for the club face, but hardened steel is not a good material for the hosel, because it is brittle.
By incorporating multiple materials into a club head, it is possible to achieve a club with many desired properties, such as a hard face, an energy damping body, and a flexible hosel. However, joining mixed materials can be problematic. For example, it is difficult to weld titanium and aluminum alloys together because of their disparate melting temperatures. Furthermore, when different materials are welded together the joint may be prone to failure because the materials on either side of the transition have different mechanical properties. In such instances, vibrations and thermal loads cannot be transmitted evenly through the joint, increasing the likelihood of failure at the joint. Other means for joining the dissimilar materials, such as adhesives and fasteners, also have shortcomings. Like welds, adhesives are prone to failure over time because of the confluence of materials with dissimilar mechanical properties. Fasteners are less prone to failure, but they add considerable weight to the club, thus requiring weight to be removed from other areas of the club to make the club head lighter and/or to meet USGA weight requirements.
Accordingly, there still remains a need for ways to fabricate golf clubs having multiple materials.